In RFID systems and short-range wireless communication systems that have been increasingly used in recent years, in order to allow a mobile electronic apparatus such as a mobile telephone to communicate with another mobile electronic apparatus or a reader/writer, communication antennas are included in these mobile electronic apparatuses and the reader/writer. Japanese Unexamined Patent Application Publication No. 2006-270681 (Patent Document 1) discloses an antenna included in a mobile electronic apparatus.
FIG. 1 is a diagram illustrating a manner in which a mobile information terminal 21 and a reader/writer disclosed in Patent Document 1 communicate with each other when they are in close proximity to each other. In the example illustrated in FIG. 1, a part of a magnetic field H of an electromagnetic wave emitted from a transmission/receiving antenna portion 26 in the reader/writer is reflected or absorbed under the effect of a metal body, such as a battery pack 25 in a terminal body 22, and is attenuated. A metal layer 30 is provided so that it is nearer to an electromagnetic wave enter side than a communication surface CS of an antenna module 10. When an external magnetic field is applied to the surface of the metal layer 30, an induced current (eddy current) occurs on the surface of the metal layer 30 and a magnetic field H1 is generated. The magnetic field H1 generates an induced current at an antenna coil 15 in the antenna module 10.
In this example, by disposing the metal layer 30 so that it covers a part of the antenna coil 15 and faces the antenna module 10 in close proximity to the antenna module 10, the transmission/receiving antenna portion 26 in the reader/writer and the antenna coil 15 in the antenna module 10 are inductively coupled via the magnetic field component H1 generated at the metal layer 30.